The type 'Microsoft.SharePoint.Portal.Analytics.UI.ReportViewerMessages, Microsoft.SharePoint.Portal, Version=12.0.0.0, Culture=neutral, PublicKeyToken=71e9bce111e9429c' does not implement IReportViewerMessages
You get this error when you have a custom ASPX page having a ReportViewer WebPart. I initially had my SSRS 2008 running in SharePoint Integrated Mode, later I changed the mode to Native and also uninstalled the SharePoint Reporting Services Add-in. Even after this, I still had this error coming up. This is what I did to fix it : added inside the tag of my SharePoint application as well as the virtual directories of ReportServer and ReportManager (these are inside C:\Program Files\Microsoft SQL Server\MSRS10.MSSQLSERVER\Reporting Services) Last but not the least, I also restarted the server for this to start working! :)